This application is based on Japanese Patent Application No. 1250/2000 and 1251/2000 filed on Jan. 7, 2000, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a method for transmitting image data, a method for relaying image data, a communication terminal, and a communication management center. The present invention is utilized for portable communication terminals for conducting image communication, such as a portable visual telephone.
2. Description of the Prior Art
Conventionally, communication terminals capable of transmitting and receiving voice and image have been proposed in order to be utilized for wire or wireless visual telephones, teleconference system, other image communication systems or the like.
In such communication terminals, images of subjects taken by a camera are transmitted as a still picture or a motional picture. At transmission of the image, image data are often highly compressed for saving communication cost. Especially, in visual telephones, a screen of the display device is relatively made to be small for miniaturizing the device and simplifying of operation thereof. By connecting a personal computer with a camera and telephone or an audio apparatus, it can be used as a communication terminal for a visual telephone or that for teleconference.
It has been proposed of communication terminals for transmitting image data together with voice, comprising a headset for speaking by the telephone, a memory card storing image data which previously are taken, a liquid crystal display device, etc. (Japanese Unexamined Patent Publication No. 6-261167).
When the above-mentioned communication terminals are used to communicate images, a communication management center for relaying data performs a variety of exchange controls for data exchange.
When case image communication is conducted by using the above-mentioned various communication terminals, the screen sizes of display devices are different depending on types of device of the destination, and thus resolutions of display are varied from each other.
When transmitting the image data from communication terminals, therefore, resolution of the image data to be transmitted is sometimes higher than that of the destination of communication. In such cases, the image is out of frame of the display screen of the destination and therefore, can not be seen easily and furthermore, communication cost increases due to data volume being large. Furthermore, in case of portable communication terminals, there is a problem that operation time becomes shortened because of waste of battery due to large data volume.
Conventionally, the communication management center only relays image data to be transmitted, and does not convert or control the image data according to the resolution of the display device of the communication terminal.
An object of the present invention is to reduce data volume to be communicated, and to suppress wasteful battery consumption in case of portable devices, by controlling for transmitting image data whose resolution is made to be matched with that of the display device of the destination at the time of transmitting image data from communication terminals.
Another object of the present invention is to reduce data volume to be communicated by converting the resolution of image data to be lowered depending on the resolution of the display device of the destination when relaying image data at the communication management center with which a plurality of communication terminals are connected.
According to a preferred aspect of the present invention, a communication terminal comprises a memory for storing a table in which data for identifying destinations of communication and resolutions of display devices of the destinations are associated with each other, an image processor for generating an image data with a resolution of the display device of the destination based on the table, and a transmission section for transmitting the image data generated by the image processor. Preferably, the terminal further comprises a sensor for taking a picture of a subject and for providing the image processor with the image data. The terminal further comprises a receiving section for receiving image data from the destination and a display section for displaying the image data received at the receiving section. The terminal further comprises an estimating section for estimating a resolution of the display device of the destination based on the received image data.
According to another preferred aspect of the present invention, a communication management center with which a plurality of communication terminals are connected and which transmits and receives data to/from each communication terminal comprises a display resolution detection section for obtaining information about the resolution of the display device of the communication terminal, a resolution conversion section for converting the image data transmitted from the communication terminal into low resolution image data based on the information about the resolution obtained by the display resolution detection section, and a transmission section for transmitting the low resolution image data obtained by converting the data at the resolution conversion section.
The other objects and features of the present invention will be more fully understood from the following detailed description with reference to the accompanying drawings.